In oil and gas production and exploration, downhole drilling through rock can be accomplished with a downhole drill through which drilling fluid, conventionally referred to as drilling mud, is pumped. The drilling fluid assists in the drilling process by, for example, dislodging and removing drill cuttings, cooling the drill bit, and/or providing pressure to prevent formation fluids from entering the wellbore.
Application of a vibrational and/or percussive effect, which can be accomplished through the regulation of drilling fluid flow, can improve the performance of the downhole drill. Examples of downhole assemblies providing such an effect include U.S. Pat. No. 2,780,438 issued to Bielstein, and Canadian Patent No. 2,255,065.
In the drawings, preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for the purpose of illustration and as an aid to understanding, and are not intended as a definition of the limits of the invention.